• Journal of Advanced Marine Engineering and Technology
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• v.32 no.5
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• pp.691-697
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• 2008

Heat exchangers are commonly used in practice in a wide range of application, from heat and air-conditioning system in a household, to chemical processing and power production in large plant. An Experimental study was conducted to investigated the fluid flow and heat transfer around four circular cylinders of in-line in a cross flow of air. The local and average heat transfer characteristics for tube banks are investigated in the present study. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluid. The in-line pitch ratio was in the range $1.5{\leq}L/d{\leq}4.0$, where L is the center distance and d the cylinder diameter, and in the Reynolds number $8,000{\leq}Re{\leq}50,000$. The local and mean Nusselt numbers were estimated. Subsequently, the heat transfer characteristics of four circular cylinders are found to exhibit a strong dependency upon the separation point of their upstream cylinders.

• Journal of Power System Engineering
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• v.12 no.5
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• pp.48-53
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• 2008

Heat exchangers are commonly used in practice in a wide range of application, from heating and air-conditioning system in a household, to chemical processing and power production in a large plant. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluids. The heat transfer characteristics of tube banks of in-line arrangements of four circular cylinders in a cross flow are compared for a range of tube locations and Reynolds numbers. The in-line pitch ratio was set up in the range of $1.5\leq L/d\leq4.0$, where L is the center to center distance and d the circular cylinder diameter, and in the Reynolds number of $13,000\leq Re\leq50,000$. The local and mean Nusselt numbers were estimated, and then. Subsequently, the heat transfer characteristics of four circular cylinders were found to exhibit a strong dependency upon the cylinder spacing and separation point of their upstream cylinders.

• Composites Research
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• v.26 no.6
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• pp.380-385
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• 2013

Characteristics of delamination factor and surface roughness by drilling condition for glass fiber reinforced plastic (GFRP) composites were investigated in this paper. An expression to quantify the delamination factor was induced by using image pixels of the entry and the experimental drilling was accomplished by fabricating several GFRP specimens in condition of minimizing the effect of vibration and heat. A method for measuring 6 points average surface roughness was applied to acquire the more reliable roughness values. The experimental results showed that the delamination factor was decreased as the feed rate was increased and it was also slightly decreased as the cutting speed was increased. Also, it was investigated that the surface roughness at inner surface of drilled holes was increased as the feed rate was increased, whereas the roughness values were not affected by the cutting speed variation.

• Journal of the Korean earth science society
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• v.22 no.6
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• pp.512-527
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• 2001

Separated flows passed complex geometries are modeled by discrete vortex techniques. The flows are assumed to be rotational and inviscid, and a new techlnique is described to determine the stream functions for linear shear profiles. The geometries considered are the snow cornice and the backward-facing step, whose edges allow for the separation of the flow and reattachment downstream of the recirculation regions. A point vortex has been added to the flows in order to constrain the separation points to be located at the edges, while the conformal mappings have been modified in order to smooth the sharp edges and to let the separation points free to oscillate around the points of maximum curvature. Unsteadiness is imposed to the flow by perturbing the vortex location, either by displacing the vortex from the equilibrium, or by imposing a random perturbation with zero mean to the vortex in equilibrium. The trajectories of passive scalars continuously released upwind of the separation point and trapped by the recirculating bubble are numerically integrated, and concentration time series are calculated at fixed locations downwind of the reattachment points. This model proves to be capable of reproducing the trapping and intermittent release of scalars, in agreement with the simulation of the flow passed a snow cornice performed by a discrete multi-vortex model, as well as with direct numerical simulations of the flow passed a backward-facing step. The results of simulation indicate that for flows undergoing separation and reattachment the unsteadiness of the recirculating bubble is the main mechanism responsible for the intense large-scale concentration fluctuations downstream.

• Journal of the Korean Arthroscopy Society
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• v.9 no.2
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• pp.206-213
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• 2005

Purpose: To evaluate the outcome of symptomatic osteochondritis dissecans of the talus treated with arthroscopic debridement and multiple drilling. Materials and Methods: Between 1997 and 2003, 14 arthroscopic debridement(group I) and 15 arthroscopic multiple drilling(group II) were performed. There are 21 male and 8 female patients. Mean age was 34.4 years(33.8 years in group I, 37.5 years in group II) and average follow-up period was 43.2 months(46.4 months in group I, 40.1 months in group II). Simple radiographs and MRI were performed preoperatively and postoperatively, and the progressive stage of the lesions was evaluated through the arthroscopic surgery. Clinical results were evaluated with ankle-hindfoot scale and scoring scale for subjective and objective functional outcomes. The results were compared between 2 groups. Results: There are 20 medial(7 in group I, 13 in group II), 6 lateral(5 in group I, 1 in group II), and 3 both-side(2 in group I, 1 in group II) lesions. According to the classification of Berndt and Harty, there are 4 stage II(4 in group I, 0 in group II), 19 stage III(9 in group I, 10 in group II), and 6 stage IV(1 in group I, 5 in group II). According to the ankle-hindfoot score, the mean score was significantly improved $53.1{\pm}2.7$ points preoperatively to $85.1{\pm}8.5$ points postoperatively in group I and $54.6{\pm}6.8\;to\;80.7{\pm}8.5$ points group II. Subjective and functional scores was also improved $49.6{\pm}10.5$ points preoperatively to $84.6{\pm}7.7$ points postoperatively in group I and $50.7{\pm}9.2\;to\;83.0{\pm}9.6$ points in group II. But there were no statistical significance between them. Conclusion: Arthroscopic debridement and multiple drilling for the treatment of osteochondral lesions of the talus showed successful results and there was no statistically significant difference between them.

• Journal of Conservation Science
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• v.25 no.1
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• pp.39-47
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• 2009

This paper reports a study on physical properties of the traditional adhesives for developing natural adhesives. This is to certify that the superiority of tradition through systematic surveys and experiments as well. We used three kinds of starches differing fermentation time(7 years, 4 years 8 months, and 2 years 8 months) which are fermented from wheat flour starches. The amylose contents, total sugar contents, crystallinity, particle size and shape, viscosity, pH, and adhesive strength were examined. The effect of fermentation time on physical properties of fermented wheat flour were studied. It was found that fermentation time effect various physical properties such as total sugar contents, amylose contents, crystallinity, viscosity, and so on.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.345-353
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• 1987

An analysis is performed to study flow and heat transfer characteristics of mixed free and forced convection about a sphere. Nonsimilar boundary layer equations which are valid over the entire regime of mixed convection are derived in terms of the mixed convection parameter, Gr/Re$^{2}$, through a dimensional analysis. The transformed conservation equations are solved by a finite difference method for the whole range of mixed convection regime. Numerical results for fluids having the Prandtl number 0.7 and 7 are presented. As the mixed convection parameter increases, the local friction coefficient and local heat transfer coefficient increases as well. For small Prandtl number, the friction coefficient is larger, while for large Prandtl number, the heat transfer coefficient is larger. Natural convection effect on the forced flow is more sensitive for small Prandtl number fluid. Flow separation migrates rearward as an increase in the mixed convection parameter. For small Prandtl number, the buoyancy effect is relatively small so that the flow separation occurs earlier.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.235-242
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• 2010

An experimental investigation has been conducted to clarify roughness effects of geothermal water scale deposited onto a heating surface upon its forced convection heat transfer characteristics. Examined was a circular cylinder, on which particles of silica scale having five different sizes are uniformly distributed. The Reynolds number was varied from 13000 through 50000. Local and mean heat transfer characteristics were measured as functions of particle size and Reynolds number. Subsequently the mean fouling resistance was estimated from those results, and its characteristics are clarified. It was found that the heat transfer of cylinders greatly varies with the fouling of geothermal water scale, especially its scale height. Further, the local and average Nusselt numbers strongly depend upon the cylinder spacing and the Reynolds number.

• Korean Journal of Cleft Lip And Palate
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• v.5 no.1
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• pp.11-20
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• 2002

정상 연구개의 근육조직에 대한 여러가지 해부학적 연구가 있어 왔지만, 구개열의 근육조직에 대한 연구는 이보다 훨씬 적었다. 또한 정상 연구개 근육조직의 형태를 잘 이해하는 것이 연구개 기능회복에 절대 필요할 것으로 사료되며 이에, 우리는 2개의 사체에서 채취한 정상상악골 및 연구개를 포함한 조직에서 연구개부위의 박리를 시행하여 근부착에 대한 해부학적 관찰을 시행하였다. 구개열환자에 있어서 연구개 근육들은 전후방적인 방향성을 가지고 있으며, 경구개 뼈의 후방 가장자리에 직접 근부착을 한다는 점에서 정상과 달랐다. 구개열 수술에 있어서 이러한 비정상적인 근부착을 박리하여 횡적방향으로 재구성하여 정중부에서 봉합하는 것이 정상적 연구개 sphincter를 만들고 연구개를 후방으로 후퇴시켜 정상적 연구개 해부구조를 재구성할 수 있는 방법이다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.916-925
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• 1988

The Navier-Stokes equations of the vorticity-stream-function form are solved numerically for the flow past a semicircular arc for Reynolds numbers in the range 0.1